The present application concerns cathode ray tubes of the apertured shadow mask type and, more particularly, a novel shadow mask cathode ray tube having a layer of high atomic number material for providing increased backscattering whereby higher peak brightness is achieved with acceptable color errors.
It is known to provide cathode ray tubes, particularly of the type utilized for color television, with a shadow mask, comprised of steel and the like materials, having a multiplicity of apertures therein. An electron beam, provided by at least one electron gun, selectively illuminates sequential ones of the apertures in the shadow mask, to provide portions of each electron beam impingent upon phosphor elements fabricated upon the rear of the cathode ray tube faceplate. A portion of each electron beam does not pass through the particular aperture at which that beam is directed, but impinges upon the shadow mask, causing localized heating thereof. Local heating of the shadow mask, especially in high-brightness portions of the display image, causes local expansion of the mask and generates color errors. Thus, one fundamental limitation upon the peak brightness of an apertured shadow mask cathode ray tube is the local heating of the aperture mask responsive to incidence of the scanned electron beam thereon.